1. Field of the Invention
The present invention relates to an IP-PBX (Internet Protocol Private Branch exchange), an IP-PBX system, and an IP terminal control program executed in the IP-PBX.
2. Description of the Related Art
An IP-PBX is a PBX (Private Branch exchange) supporting IP (Internet Protocol) communication. An IP-PBX system is known, in which an IP terminal such as an IP phone and a personal computer carries out IP communication by using the IP-PBX through a local area network (LAN).
Japanese Laid Open Patent Application (JP-P2002-290633A) discloses an exchange used for an IP terminal carrying out IP communication through a private line or the Internet. The exchange has an identifying unit, a rate calculating unit, a rate information storing unit, and a notifying unit. When this exchange (receiving site) receives a request for IP communication from another exchange (initiating site), the identifying unit identifies an IP address of the other exchange based on the IP address included in the request. When an IP terminal accommodated by the other exchange carries out IP communication by using the line connected to the exchange of the receiving site, the rate calculating unit calculates the rate of the IP communication. Here, the rate of the IP communication is calculated for every IP address identified by the identifying unit. The rate information storing unit stores information about the rate calculated by the rate calculating unit for every IP address. The notifying unit notifies the other exchange (initiating site) of the information about the rate stored in the rate information storing unit.
Japanese Laid Open Patent Application (JP-P2002-354116A) discloses a virtual private branch exchange. The virtual private branch exchange includes exchanges provided by communication providers, WANs (Wide Area Networks), LANs (Local Area Networks), communication line networks, local phones, subscriber's telephone stations, and a call control apparatus. The call control apparatus treats the local phones and the subscriber's telephone stations as extension phones, and provides voice communication and a variety of extension services for the local phones and the subscriber's telephone stations.
In the conventional IP-PBX system, an IP terminal management unit carries out the functions of interface (e.g. protocol conversion) between exchange control software and IP terminals. There are two methods to achieve the management of the IP terminals, “card mode” and “built-in software mode”. In an IP-PBX system for the “card mode”, an IP terminal control card plugged into a card slot manages the IP terminals. In an IP-PBX system for the “built-in software mode”, a software-based IP terminal management unit manages the IP terminals, executed by a central processing unit.
According to the IP-PBX system for the “card mode”, a plurality of IP terminal control cards are plugged into different card slots. When an IP phone logs in to the IP-PBX system, the exchange control software selects one IP terminal management unit to be used for managing the IP phone, and stores a port number associated with the one IP terminal management unit. When the exchange control software transmits a control signal to an IP phone, the exchange control software designates a port number associated with an IP terminal management unit managing the IP phone.
According to the IP-PBX system for the “built-in software mode”, only one IP terminal management unit operates in that system. Therefore, when an IP phone logs in to the IP-PBX system, the IP terminal management unit to be used for managing the IP phone can be determined uniquely. A control signal for controlling the IP phone is transferred to the one IP terminal management unit.
It is not possible to merely combine an IP-PBX system for the “card mode” with an IP-PBX system for the “built-in software mode”, because there is no way to specify the IP terminal management unit for the “built-in software mode”. That is to say, when an IP phone logs in to such an IP-PBX system, the IP terminal management unit for the “built-in software mode” can not be selected.
Also, when trying to expand IP phones in an IP-PBX system for the “built-in software mode” and the number of the IP phones being larger than the capacity of the IP terminal management unit, an IP-PBX system for the “card mode” must be introduced in place of the IP-PBX system for the “built-in software mode”. It is necessary to prepare IP terminal control cards which manage not only the expanded IP phones but also IP phones originally managed by the IP terminal management unit for the “built-in software mode”.